The present invention relates to a projector such as an LCD projector that is capable of adjusting a position of a projected image on a screen. Particularly, the present invention relates to a reflection type projector that is provided with a reflection type light modulating element.
Japanese Patent Provisional Publication No. Hei 5-27324 discloses an LCD projector that is capable of adjusting a position of a projected image on a screen. The disclosed LCD projector includes a transmission type LCD panel through which parallel illumination light from a light source is transmitted, a condenser lens and a projection lens. The illumination light is modulated by the LCD panel and projected onto the screen through the condenser lens and the projection lens.
The condenser lens and the projection lens are mounted on an adjusting mechanism so that the lenses are moved, as one unit, in a direction perpendicular to the optical axis. Movement of the lenses by the adjusting mechanism shifts the position of the projection area on the screen without changing a position of the main body of the projector and without distorting the projected image.
However, the conventional LCD projector that employs the transmission type LCD panel has a problem in that the light efficiency, which is defined as a ratio of the maximum output light quantity from the LCD panel to an incident light quantity to the LCD panel, deteriorates as the resolution becomes higher in a constant panel size. The transmission type LCD panel must include opaque portions for arranging driving circuits. In particular, an active matrix type LCD such as a TFT (Thin Film Transistor) has a switching element such as a transistor for an each pixel element. When the resolution becomes higher in a constant panel size, the pixel size and the driving circuit size become smaller. However, the size of the driving circuit can not be reduced at the same ratio as that of the pixel, and accordingly, the ratio of the opaque area increases, which deteriorates the light efficiency.
One solution to increase the resolution without deteriorating the light efficiency is adoption of a reflection type light modulating element such as a reflection type LCD panel or a DMD.TM. (Digital Micromirror Device.TM.). The DMD.TM. has many micromirrors that are two-dimensionally arranged. The reflection angle of each micromirror is independently controlled. Since the driving circuits can be arranged on the back side of the reflection surface in the reflection type light modulating element, it is free from the light efficiency deterioration due to increasing of the resolution.
The reflection type light modulating element requires an inclined arrangement of the optical elements of the projector. In the inclined arrangement, an illumination light from a light source is incident on the reflection type light modulating element along an incident light path that is inclined with respect to the light modulating element, and the reflected light is incident on a projection lens along a reflected light path that is different from the incident light path. If the adjusting mechanism disclosed in the publication is used in the reflection type projector, and the position of the adjusting mechanism that includes the projection lens and the condenser lens is changed, the reflected light from the reflection type light modulating element is not efficiently incident on the projection lens and it may lower the luminance in the projected image and/or part of the projected image may lost. It should be noted that the efficiency is defined as a ratio of the projected light amount to the incident light amount, and it depends upon a positional relationship between a pupil of the light source and an entrance pupil of the projection lens. When these pupils are optically conjugate, the efficiency reaches a maximum value. When the pupils are not conjugate, the aperture stop of the projection lens shades part of the light, decreasing the efficiency. Accordingly, the adjusting mechanism disclosed in the publication is not applicable to the projector that employs the reflection type light modulating element.